Stabilization of wood and wood products with vinyl compounds



Feb. 12, 1963 ENAGA 3,077,419

D. L. K STABILIZATION OF WOOD AND WOOD PRODUCTS WITH VINYL COMPOUNDS Filed Feb. 5, 1958 Woool Swe//fng Swe//fng ayen/ /m e 075,7 V/r/ y/ /QromO/fc /O -7 9 /m/oreyn n /rroa//cy//o' n /rra o//a /fon so arc@ Fijwl Wcvool we //f 'ng a no /mprekgna/'on /rr 0//0 fion /m/orey/van /rr aa//a /fon so aree Fay? INVENTOR.

` Dua/7e L. Kenoya ,Q TORNE Y 3,677,419 STABILE/@KUN F WUD AND Vi/60D PRDUCTS WETH VENYL CMPUNDS Duane lL. Menage, Midland, Mich., assigner to The Dow Chemical Company, Midland, Mich., a corporation of Deiaware Filed lieb. 5, l95, der. No. 713,318

il; Claims. (Cl. ifi-59) This invention relates to stabilization of wood and to natural and artificially formed lignocellulose containing materials and more particularly to a new and useful method for the stabilization of wood and wood-like products against dimensional change and to compositions for effecting such stabilization.

It is well known that materials made up entirely or predominantly of cellulose fibers expand and contract with variations in humidity in the ambient atmosphere. in wood, for example, such swelling and shrinking is accompanied by warping and checking. These properties are particularly undesirable when wood is used as a structural material. Wood undergoes an increase in dimension upon absorption of moisture from the atmosphere and a contraction when moisture is given up to the atmosphere. in a very humid atmosphere the increase in swelling continues until a moisture content of between 28 and 30 percent is reached. This moisture content is known as the liber-saturation point. Below the bersaturation point the water enters the line capillary structure of the cell walls and aiiects the dimensions of the wood. Above this moisture content the water enters the cell cavities or the coarse capillary structure. The water present in the coarse capillary structure of the wood is called free water and does not affect the swelling and shrinking under normal conditions.

Stabilization of wood against dimensional changes has been attempted heretofore with only limited success. Some of the more important general methods which have been employed are (l) coatings, both external and internal; (2) deposition of bulking agents in the cell walls; (3) decreased hygroscopicity plus bulking; and, (4) chemically cross-linking the cellulose molecules, thereby reducing the degree to which wood can swell. An eX- amplc of the cross-linking method of dimensional stabilization is the treatment of Wood with formaldehyde. The stabilization is obtained by a reaction between formaldehyde and the hydroxyl groups of the cellulose molecules connecting together the latter by cross-bridges of acetal linkages. One of the principal disadvantagesof the formaldehyde treatment is that it requires anhydrous conditions and Very corrosive mineral acids as catalysts, resulting in extensive hydrolytic degradation of the wood. An example of the bulking technique for the stabilization of wood is the impregnation of the swollen wood with a thermosetting resin. In this method, an unpolymerized resin is permitted to diiiuse into the cell walls and the treated wood heated to polymerize the resin within the cell walls to form an irreversible polymerized compound which holds the wood in a swollen state. This treatment, however, changes the physical properties or" wood, notably its resiliency and shock resistance. Furthermore, resin treated wood is very heavy and very hard. The resin process has other disadvantages from the treatment standpoint in that it is only commercially practicable for veneer or plywood. A more recent theory under which wood is stabilized is by reduction of hygroscopicity plus bulking. The theoretical principle is thought to be a replacement of some of the hydroxyl groups of the cellulose structure by reaction with the treating material plus bulking the cell walls by the specific volume of the treating material. An example of this technique is acetyla- 3,977,4l9 Patented Feb. 12,

2 tion with acetic anhydride and catalysts and swelling agents such as pyridine or dimethylformamide. This procedure is not commercially practical for large cross section treatment.

It is, therefore, an object of this invention to provide a new and novel method for the dimensional stabilization of wood and other lignocellulosic materials. A further object is` to provide a method for reducing the shrinkage and swelling of wood. A still further object is to provide wood resistant to warping and checking. A still further object is to provide a dimensionally stabilized wood which when stabilized is free of the degradation caused by using known crosslinking agents and catalysts. These and other objects will become evident from the following specication and claims.

FIGURE 1 represents a schematic diagram of the method employed in accordance with the present invention to accomplish the dimensional stabilization of lignocellulosic materials;

FIGURE 2 represents a modified procedure in accordance with the present invention and accomplishes the dimensional stabilization of lignocellulosic materials.

in accordance with the present invention, it has been found that effective dimensional stabilization of any wood can be obtained by treatment thereof with a non-leachable, non-swellable, insolubilizable compoundH having radiation-activatable reactive groups and irradiating the so treated wood under conditions whereby a significant proportion of the treating compound isretainedmin the woods by reaction with the lignocellulosic constituent or otherwise. The resulting cellulosic product, containing from l0 to 50 percent by weight or more of thefco'mpound in the form of a nonfleachable', non-swellable Water insoluble product associated with the wood, isfound to be stabilized against dimensional changes, warping and checking resulting `from effects lof moisture. Although the amount of compound desirable in the wood structure will vary with the intended use of the stabilized material, the presence of 15 to 3VO `percent by `weight of the cornpound is considered-preferable for most purposes.

By employing the treatment of the present invention, wood may be dimensionally stabilized or made resistant to swelling and shrinking without altering greatly its physical properties. Furthermore, anhydrous conditions are not required in carrying out `this process. The present treating compoundsmay be introduced in tothe `wood Yfrom substantially any wood-swelling solvent such as aqueous or organic solvent solutions. The subsequent irradiation provides `a degree of stabilization or reduction in `swelling ofifrom about l0 to 70 percentcr more. The percent reduction in swellingdepends in part on the weight of the compounds retained by the wood. The process of the present invention is applicable to commercial application where relatively large cross-sections `are to be stabilized.

In accordance with this invention, `Wood or a wood product is immersed in the impregnate or in asolution of the impregnating compound dissolved or dispersed in a wood swelling agentto `assist in the penetrationof lthe former into the cell wall and into intimate contact with the lignocellulosic structure. Alternatively, the wood may be swelled with a wood swelling agent and then immersed in the impregnant or a solution of the impregnant. This immersion or kimpregnation step may be conducted at atmospheric pressure or at subor super-atmospheric pressure, and at room temperature or slightly .elevated temperatures. Such impregnation methods are `well known to those versed in the art of Wood preservation. It is generally preferred to operate at a temperature in the range of about from 15 to 85 C. ,Such temperatures give good results, although` somewhat higher `and lower temperatures may be employed without materially anemie alecting the results. The treating compound may be applied from aqueous solution, but solutions in organic solvents may also be employed with equal success when good recovery permits reuse of the solvents. ln some cases the treating compound may also serve as the swelling agent. Suitable organic solvents include those which swell wood such as methanol, ethylene glycol, methyl ether, N-methylpyrrolidone, dioxanes, dimethylformamide, diethylene glycol, diethylene glycol methyl ether, pyridine, n-butylamine, piperidine, morpholine, 4-picoline, 2-picoline, diethylamine, 2,6-butadiene, aniline, acetone, and mixtures thereof, or aqueous solutions or aqueous mixtures thereof.

Various impregnating compounds have been employed in accordance with the present invention and found to be satisfactory. Some of such compounds are the vinyl and vinyl aromatic compounds such as dichloro styrene, vinylphenylacetic acid and vinylphenyl acetonitrile; that is to say one can employ as the impregnating agent a vinyl compound having the formula CE=CH1 wherein Y represents a member selected from the group consisting of hydrogen, halogen, methyl, carboxymethyl, and cyanomethyl; and, wherein X may be chlorine when Y is chlorine, otherwise X is hydrogen.

The concentration of impregnating or treating compound in the solution will depend in part on the specific treating compound, the solvent, the temperature, and the type of irradiation. Generally, a -30 percent solution has been found to be convenient, although any suitable concentration may be employed.

The preferred conditions of treatment will depend on the particular wood or wood product, the dimensions thereof, the treating compound, the type and degree of irradiation, the solvent and in some instances other factors. After an immersion period in the treating solution, the impregnated wood is cured by exposure to ionizing radiationV for a suitable period of time to bring about a reaction, bonding or other association between the treating compound and the cellulosic material so that a significant proportion of the treating compound is retained within the wood (lignocellulosic) structure. In selecting a suitable radiation source, high energy particulate radiation or high energy electromagnetic radiation may be employed. Thus, one may employ atomic particules, neutrons, photons, gamma rays, X-rays, electrons, deuterons, and fission fragments from nuclear reactors or accelerators, or from articial or natural radio active isotopes. Good results have been obtained by irriadiation from sources emitting from 102 to 107 fads/sec. such as a 2 mev. (million electron volts) source at beam currents up to 145 microamps. Good results have also been obtained by irradiation from a cobalt 60 source at dose rates up to 650,000 rads/hr. (698,750 reps/hn). Wood or Wood products may be irradiated up to a dose of 107 rads. Irradiation at doses greater than 107 rads will probably cause severe degradation of the cellulosic structure.

After the curing step, the unassociated treating agent and swelling agent may be removed from the wood. The result of .this series of operations is that a significant residue of the stabilizing compound is reacted with or in some manner associated with and retained in the wood structure, impar-ting thereto the property of resistance to dimensional change resulting from variations in ambient humidity.

In one procedure for treating wood to obtain dimensional stabilization data, an air-dried pinderosa pine sapwood block, for example, is weighed and accurately measured in the tangential direction. The wood is then impregnated with one of the treating compounds by vacuum impregnation at an appropriate temperature and pressure. In many instances the impregnate is a solution of the compound dissolved or dispersed in a wood-swelling agent, such as dimethylformamide. Subsequently, the block is removed from the solution and may be sealed in a waterand air-impervious, plastic material to prevent loss of treating solution. The so packaged wood is irradiated to from 102 to 107 rads by, for example, a 2 million-volt-electron beam (Van de Graal? generator) with a current of 5.6 to 56 microamps. with the wood in the electron beam about 20 percent of the time. In other instances, the impregnated wood is irradiated in a cobalt 60 source at a dose rate of about 156,000 rads per hour. Following the irradiation, the wood, if sealed in the plastic bag, is removed from the bag and conditioned in air to remove unreacted volatile solvents and/or unreacted or solvent-soluble compounds, and for purposes of laboratory comparison leached with running distilled water until the pH of the leached water is the same as that of the untreated concurrently leached controls to remove any unassociated compound or water-soluble solvents.

For the purposes of comparison and to determine the degree of dimensional stability, the leached wood pieces are oven dried at *l05 C., measured along the tangential direction, re-weighed, soaked in water, and remeasured. Prom the difference in the dried weights before and after treatment with the compounds, the percent compound in the treated wood can be determined. Prom the diderence in tangential dimensions of the treated soaked wood and the treated oven-dried wood, the percent swelling of the treated Wood can be determined. Similar rneasnrernents are made on controls of untreated wood. From the data, the degree of dimensional stabilization or reduction in swelling can be calculated according to the following equation:

Percent reduction in swelling [Percent swelling of Percent swelling of untreated wood treated wood Percent swelling of untreated wood The following examples are illustrative of the present invention, but are not to be construed as limiting the same.

Example l Clear ponderosa pine sapwood wafers or blocks measuring 1.375 inches radially X 2 inches tangentially x 0.25 inch longitudinally were weighed and accurately measured along the tangential direction. Certain of these wafers were immersed in dimethylformamide containing 20 percent by weight of dichlorostyrene by subjecting the wood blocks first to a vacuum of 10 mm. of mercury for ten minutes and then introducing into the evacuated charnber the dimethylformamide dichlorostyrene solution, and thereafter raising the pressure to atmospheric pressure. The wafers were held immersed for about 10 minutes and then were packaged in small plastic polyethylene bags to prevent loss of treating solution. The so-packaged wafers were then subiected to gamma irradiation from a cobalt 60 source at a dose of 0.93X 107 rads. Following the irradiation, the wafers were removed from the polyethylene bags, conditioned in air to remove any unreacted volatile solvents, monomers or compounds and then leached in running distilled water for three days. The blocks were then carefully dried to below fiber saturation point to prevent checking and then oven-dried at 105 C. for 24 hours. The wafers were then measured and weighed at the oven-dried conditions to determine the retention and the tangential dimensions, and then were re-swelled in water to obtain the swollen dimensions. The dichlorostyrene retained in the wood was shown by a weight gain of the wafer of 28.4 percent. The meas- .ured percent reduction in swelling was 18.1 percent.

uring 1.375 inches radially x 2 inches tangentialiy x 0.25 inch longitudinally were weighed and accurateiy measnocellulosic materials which comprises the steps of swelling the said lignocellulosic material Vwith an organic swelling agent, while simultaneously impregnating the said material with a'viiiyl compound having the `formula ured along the tangential direction. Certain of these X wafers were immersed in methyl alcohol containing 26 CH CH 2 percent by weight of dichlorostyrene by subjecting the Y wood blocks rst to a vacuum of mm. of mercury for ten minutes, and then admitting the impregnating solution. The pressure was thereafter raised to atmospheric 10 pressure. The blocks were then irradiated in a Van de Whelzeu? Y represents a member Seleeted from the group Graaff generator source to a dose of 093x1117 rads, then eonslstmg 0f hydrogen, 1121105611, methyl, carboiiymethyl carefully removed from the bags, conditioned, leached, ane eyanellethyl? and; Whefem X may be Chlofme when dried to below fiber saturation point to prevent checking Y 1S ih lollne, Otherwise X 1S hydrogemand, lrradiating and than Ovemdried at 105 C for 24 boum The meas 15 the so impregnated swelled lignocellulosic material with ured percent reduction in swelling was 53.3 percent. from 102 t0 107 rads 0f hlgh energy ionizing radiation for from 1 sec. to about 24 hours. Example 3 6. A process for the dimensional stabilization of lig- In the manner of Example 1, employing vinyltoluene nocellulosic materials which comprises the steps of swellin place of dichlorostyrene and electron irradiation from 2O ing the Said hgHOCEQIOSC material With an O fganlc SWCH- a Van de Graafl machine at a dose of 0.93 10Y rads 111g agent, 1II 1preg 11a t1I1g the said material. with d ichlorothere was obtained a 15.2 percent reduction in swelling styrene and lffadlallg th? Said S0 eed matel1a1- ll/ 1th and a weight increase 0f 10,6 percent, from 102 to 107 rads of high energy particulate radiation E lo 4 16 for from 1 sec. to about 24 hours.

xamp s m 25 7. A process for the dimensional stabilization of lig- In the manner of the foregoing examples, substituting nocellulosic materials which comprises the steps of swellthe following compounds and swelling agents, there was ing the said lignocellulosic material with an organic swellobtained the following results. ing agent, impregnating the said material wtih dichloro- Treating Compound, Radiation Type Percent Percent Erample No Swelling Agent Percent by Weight and Dose in Reduction Weight Rads1 lnSwelling Increase Dimethyltormainidc. QOperccnt Vinylphenyl- E0.93 10 35.5 14.4

acetic Acid.

d 39.6 18.6 43.0 22.9 o- 15.1 15.7 percent Viuylphcnyl. 22. G 18. l

Acetonitrilc. do 41.2 20.9 G0.s3 102 24.6 12.2 rio Gossxlci 34.2 20.4 percent V inylphcnyl E 105 36. 4 23. 4

Acctonitrile.

i 40.8 25.0 69.8 44.2 ass 36.8 57.1 47.2

1 E-Elcctron from a Vrin de Graaff generator; G-Garnma cobalt 60.

I claim:

1. A process for the dimensional stabilization of lignocellulosic materials which comprises the steps of swelling the said lignocellulosic material with an organic swelling agent, impregnating the so swelled material with a vinyl compound having the formula CH=CH2 Y wherein Y represents a member selected from the group consisting of hydrogen, halogen, methyl, carboxymethyl and cyanomethyl; and, wherein X may be chlorine when Y is chlorine, otherwise X is hydrogen; and, irradiating the so impregnated swelled lignocellulosic material with from 102 to 107 rads of high 4energy ionizing radiation for from 1 sec. to about 24 hours.

2. A process as set forth in claim 1 wherein the vinyl compound is dichlorostyrene.

3. A process as set forth in claim 1 wherein the vinyl compound is vinylphenylacetic acid.

4. A process as set forth in claim l wherein the vinyl compound is vinylphenyl acetonitrile.

5. A process for the dimensional stabilization of ligstyrene and irradiating the said so treated material with from 102 to l0I rads of high energy electromagnetic radiation for `from 1 sec. to about 24 hours.

8. A process for the dimensional stabilization of lignocellulosic materials which comprises the steps of swelling the said lignocellulosic material with an organic swelling agent, impregnating the said material with vinylphenylacetic acid and irradiating the so impregnated material with from l02 to l()7 rads of high energy electron radiation for from 1 sec. to about 24 hours.

9. A process for the dimensional stabilization of lignocellulosic materials which comprises the steps of swelling the said lignocellulosic material wtih an organic swelling agent, impregnating the said material with vinylphenylacetic acid a-nd irradiating the said so treated materal with from 102 to 10i7 rads of high energy electromagnetic radiation for from 1 sec. to about 24 hours.

10. A process for the dimensional stabilization of lignocellulosic materials which comprises the steps of swelling the said lignocellulosic material with an orga-nic swelling agent, impregnating the said material with vinylphenyl acetonitrile and irradiating the said so treated material with from 102 to 10" rads of high energy electron radiation for from 1 sec. to about 24 hours.

11. A process for the dimensional stabilization of lignocellulosic materials which comprises the steps of 7 swelling the said lignocellulosic material wtih an organic swelling agent, impregnating the said material with vinylphenyl acetonitrile and irradiating the said so treated materal wtih from 102 to 10rz rads of high energy .electromagnetic radiation for from l1 sec. to about 24 hours.

Klatte Oct. 2, 1917 Shannon July 4, 1944 2,462,555 Rosenthal Feb. 22, 1949 2,670,483 Brophy Mar. 2, 1954 2,790,736 McLaughlin Apr. 30, 1957 2,793,970 Jeppson May 28, 1957 OTHER REFERENCES Sun: Modern Plastics, vol. 32, No. 1, September 1954, pp. 141-144, 146-148, 150, 229-233 and 236-238.

BNL 389 (T-73) Progress Report on Fission Products Utilization VH, Brookhaven National Lab., May

1956, esp. page 19. 

1. A PROCESS FOR THE DIMENSIONAL STABILIZATION OF LIGNOCELLULOSIC MATERIALS WHICH COMPRISES THE STEPS OF SWELLING THE SAID LIGNOCELLULOSIC MATERIAL WITH AN ORGANIC SWELLING AGENT, IMPREGNATING THE SO SWELLED MATERIAL WITH A VINYL COMPOUND HAVING THE FORMULA 